Molded plastic valves are well known in the art. The increasing use of plastic pipe and tubing by gas utilities has made it necessary to seek improved valves for use with these plastic materials.
Rotary type valves have long been known and many modifications have occurred over the years. Of particular note is U.S. Pat. No. 4,511,120, issued Apr. 16, 1985, to Connelly, et al., and assigned to Kerotest Manufacturing Co. Service valves, such as a ball valve or a plug valve, of molded polyethylene material generally include a one-piece body having a valve seat with first and second passageways opening into the seat. A rotary member is positioned in the valve seat and a passageway through the rotary member is movable between a closed position where the flow between the first and second passages of the valve body is blocked and an open position where the passage through the rotary member is aligned with the passages in the valve body to permit flow between the first and second passages through the rotary member. The rotary member is provided with seals which seal against the walls surrounding the valve body passages to shut off the flow through the passages when the rotary member is turned to the closed position.
In order to prevent leakage between the body and the rotary member, annular O-ring seals are utilized. It is also desirable to test the seals between these components under pressure prior to actual use of the valve. Previously developed valves have utilized an integral stem and plug arrangement where a stem extends upwardly from the plug and is connected to an adapter or nut for turning the stem. In such previously developed valves, the nut forms part of the seal for the valve, and therefore the nut must be installed prior to testing of the valve and seals for leakage. A need has thus arisen for a plastic service valve in which testing of the valve body and rotary member for leaks can be performed independently of additional structure which may form part of the valve and which would interfere with leakage detection during testing. It is desirable that testing be accomplished with the rotary member in both the open and closed positions for a complete testing of the valve.
The adapter structure utilized for actuating the valve, because of its upward projection from the valve body, is exposed to external impact and rotational forces for imparting motion to the rotary member. The adapter may include an operating nut which is turned by the user of the valve for controlling the position of the rotary member. In order to provide feedback to the user that excessive rotary torque is being applied to the nut, previously developed plastic valves have included breakaway tabs. However, once the tab has been broken, the user no longer is provided with the safeguard of knowing if excessive torque is being applied to the nut. A need has thus arisen for a nut in a plastic valve which provides additional feedback information to the user that excessive torque is being applied to the nut during valve operation.